The present invention relates to a storage mechanism and more particularly to the update of contents stored in shared storage.
Normally, a data center connected to the Internet has a plurality of layers.
FIG. 15 shows the configuration of the so-called front-end layer, i.e., the layer nearest to the Internet. A load balancer 51 distributes accesses from Internet 50 to a plurality of servers 501 through 505.
The servers 501 through 505 provide services such as Web, FTP, etc. The servers 501 through 505 are respectively equipped with storage devices 511 through 515 having one or more hard disks. The storage devices 511 through 515 store the contents of each Web site, FTP site, etc. (hereafter simply referred to as a site) processed by the data center.
A managing server 40 managing the servers 501 through 505 has a storage device 41 having one or more hard disks. The storage device 41 contains the master copy of the site contents. When the master copy is updated, the managing server 40 updates the contents of the servers 501 through 505. (Hereinafter, the updated contents are referred to as the “new contents” and the contents before update are referred to as the “old contents”.)
Various kinds of errors may occur if the servers 501 through 505 are accessed while the contents are being updated. Therefore, the managing server 40 updates the contents according to the following procedure.
First, the setting of the load balancer 51 is changed to detach the server 501 from the site. (Thereafter, no accesses are transferred to the server 501 from the Internet 50.)
The managing server 40 copies the new contents (or the difference between the old and new contents) from the storage device 41 to the storage device 511 of the server 501.
Finally, the setting of the load balancer 51 is restored to reattach the server 501 to the site. The managing server 40 repeats the above-mentioned three steps for the servers 502 through 505 to update the contents of the entire site. Since the servers 502 through 505 are updated one by one, the site can be accessed during the update. The site performance degrades just by the performance of one of the servers 501 through 505.
Recently, the density of the servers 501 through 505 has been increasing. However, the improvement of the density becomes restricted if the respective servers 501 through 505 contain storage devices 511 through 515. Also, in recent years, electric power consumption has increasingly become an issue for data centers and sites that manage a plurality of servers as mentioned above. Therefore, there has been an increasing demand for reducing the power consumption.
The aggregation of storage devices is disclosed in, for example, the following documents:
http://www.hitachi.co.jp/Prod/comp/storage/diskarray/what#san/nas.html
(hereafter referred to as document 1) and
ftp://download.intel.com/ebusiness/pdf/prod/infiniband/wp012501.pdf
(hereafter referred to as document 2). As described in these documents, it is known that a plurality of servers having no local storage devices can share one storage device via, for example, a network. Since each server is not provided with a storage device, it is possible to decrease the electric power consumed by these servers (and the power needed for cooling the computer system), and it is also possible to improve the density of arranging servers in, for instance, a data center by reducing their size.
While the latter prior art disclosed in documents 1 and 2 has advantages over the prior art as shown in FIG. 15, updating the contents stored in the storage device becomes a problem. Specifically, in the latter example where a plurality of servers share a volume of the storage device being shared, when updating contents of the volume in this case, all servers accessing that volume must be detached from the site. This greatly decreases the site performance or even makes the whole site unavailable.
To solve this problem, the new contents need to be stored in a volume separate from the volume of the old contents, and then the volume accessed by each server is changed from the latter volume to the former volume. In this case, separate volumes for the new and old contents are needed. The volume for the new contents must be allocated on a physical storage device, increasing the capacity needed on the storage device. Therefore, even if the server does not contain storage devices, the capacity or the number of storage devices increases. This prevents the decrease in the total power consumption of the server and storage devices, and the increase in the density of the servers from the reduction in their size.